In electrical power supply networks, harmonics is a term used to describe the shape or characteristic of a distorted non-sinusoidal voltage or current waveform with respect to the fundamental frequency sine wave. Harmonic currents generated by non-linear loads, such as power electronic equipment, arc furnaces, saturating inductances, and other types of solid-state load devices, are injected into an electric power supply network. Such injected harmonic currents distort the supply source in an undesirable manner. These harmonic currents are sometimes referred to as contributions from the customer.
Harmonic currents cause harmonic voltage drops when harmonic currents generated by the customer's non-linear loads are injected into the electric power supply network. Accordingly, the supply voltage at the customer is no longer sinusoidal. Harmonic currents that distort the sinusoidal supply voltage (and/or supply current) in an electric power supply network give rise to several problems, such as: creating distorted supply voltages to loads, which in some cases cause overheating of customer equipment, or additional losses and overheating of network equipment, creating additional losses in transformers and/or cables, inducing electromagnetic interference onto neighboring telecommunication circuits, creating light flicker, causing malfunctioning of metering, current and/or voltage transducers, and/or causing malfunctioning of protection systems.
The resultant distorted load current, when measured or metered at the connection point of the customer to the electric power supply network, consists of two components; that due to contributions from the customer's non-linear load, and that due to contributions from the power system. Accordingly, it is desirable to distinguish between these two components, particularly without disconnecting the customer from the network to perform conventional load testing or analysis.
Other customers may be connected to the same connection point, or relatively close to the connection point, of the customer having loads that generate undesirable harmonic currents. Since these harmonic currents are injected into the electric power supply network, the supply voltage (and/or current) provided to the other customers may be distorted by the customer having the non-linear loads (that do cause harmonics). Accordingly, these other customers may not receive an acceptable level of power quality from the electric power supply network, thereby degrading performance of their load devices.
These other customers may have linear loads (that do not cause harmonics) and/or non-linear loads (that do cause harmonics). In some situations, the non-linear loads of the other customer, by themselves, would not otherwise cause significant unacceptable distortions in the supply voltage. However, the distortions from both customers may have a cumulative effect on the total harmonic distortion in the supply voltage. Accordingly, it is desirable to distinguish between harmonic distortion contributions from a plurality of customers supplied from the electric power supply network.
Furthermore, traditional testing methods provide results that are problematic at best. That is, since the non-linear loads may be on or off at the time of testing, it is problematic whether or not testing results accurately reflect harmonics of interest. For example, if the test is conducted during the day, harmonics induced by solid-state lighting ballasts may or may not be on at the time of testing. In a large plant, determining when a particular solid-state controlled motor is operating requires coordination. If many solid-state controlled motors are in the plant, coordination becomes even more difficult.
Furthermore, even if all of the solid-state controlled motors could be simultaneously operating during the test, or if testing results of individual motors could be computationally aggregated, is the resultant harmonic contribution from all of the solid-state controlled motors a reasonable representation of actual operating conditions of the plant? Accordingly, it is desirable to be able to test for harmonic contributions on an ongoing basis, and to differentiate harmonic contributions from individual customers when multiple customers are connected at a common connection point (or relatively close together).